Our law firm defends a number of DUI (drunk driving) cases in Pennsylvania involving blood evidence. As most of my readers already understand, the legal Blood Alcohol Content (Concentration) Limit (BAC) in Pennsylvania, and all jurisdictions including New Jersey, is .08. While the prosecution doesn’t need to establish a specific BAC concentration to convict an individual of drunk driving in Pennsylvania (General Impairment DUI – See Section 3802(a), it will need this evidence to prosecute an individual for more serious DUI offenses under the DUI statute (See Title 75 § 3802(b) and (c)).

How is BAC calculated in Pennsylvania?

There are 2 generally accepted ways in which the prosecution (District Attorney) can establish a specific BAC level—a breathalyzer or a blood draw. I’ve written previous articles on breath test analysis and Henry’s Law and encourage you to read the article, watch the video, and visit my free download section on this topic which is discussed in my free book—5 Ways to Fight & Win Your Pennsylvania DUI.While breath testing is much more convenient and much less intrusive, blood provides a much more specific BAC level because it typically does not require any type of conversion calculation to arrive at a BAC level. It’s important to realize, however, that there are specific procedures for blood draws in Pennsylvania. In addition to these pre and post procedures (non-alcoholic cleansing solution and storage temperature), laboratories within the Commonwealth must test whole blood as opposed to blood serum.

Blood Serum vs. Whole Blood – Conversion

Blood serum is that which remains after cells and fibrin, the bloods clotting agent, are separated from the plasma. Serum is less dense than whole blood and therefore the weight per volume of alcohol in serum will exceed the weight per volume of alcohol in whole blood. Given this difference, the lab must use an acceptable conversion factor to convert serum BAC to whole blood BAC.

The prosecution (district attorney) can’t convict a defendant of drunk driving in Pennsylvania under DUI subsections of the statute (3802) which specifically include a BAC level within the elements of the offense utilizing solely blood serum analysis. If the prosecution intends to introduce blood serum it must not only utilize a conversion factor but inform the fact finder (judge or jury) that a chemical analysis was performed on the serum as opposed to the whole blood.

In Pennsylvania, the case of Commonwealth vs. Newsome dealt with this issue. In that matter, the defendant was arrested and taken to a local hospital where his serum was tested as opposed to his whole blood. At the trial the Commonwealth introduced evidence of high-end conversion factor and low-end conversion factors. Further, it introduced a laboratory technician who testified that he used the conversion factors to arrive at a whole blood BAC based on plasma (serum) BAC utilizing this factor.

While the defendant in the Newsom case filed an appeal, the Pennsylvania Superior Court denied the appeal and specifically stated that the defendant didn’t present any evidence to support his assertion that the conversion factor utilized was unreliable. In its opinion the court stated that the conversion factor represents a statistical norm which provides for a certain degree allowable variance due to the differing ratios between serum and whole blood.

The defense must assert the argument to contest the validity of a conversion factor?

Prior to the Newsome case, defense counsel could argue that the absence of a test to determine a defendant’s hematocrit ratio, in and of itself, established reasonable doubt with regards to BAC. After the Newsome decision, however, Pennsylvania has generally accepted that the standard conversion factor will allow the Commonwealth to meet its burden of proof unless the defendant can establish an abnormal hematocrit level, which will call into question the validity of the standard conversion factor. In a DUI prosecution involving the conversion of serum to whole blood, it is the defense’s obligation to put on evidence to challenge the weight of the Commonwealth’s use of the conversion ratio, which would otherwise relieve the Commonwealth from having to present evidence to the court with regards to the reliability of those ratios.